915iS Current Availability

by Micheal Fletcher in 915iS Technical Questions 6 years ago

I am building a Sling 4 TSi With a Rotax 915. I will be using the VPX Pro. I am trying to find out what the maximum current available from the built in generators. Can anyone help?

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Re: 915iS Current Availability

by RotaxOwner Admin » 6 years ago

RotaxOwner Admin

59 1.58k 13.8k

Nice plane! The two onboard generators produce 30 Amperes and 15 Amperes, respectively.

Thank you said by: Micheal Fletcher

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Re: 915iS Current Availability

by Bill Hertzel » 6 years ago

Bill Hertzel

13 1.95k 7.96k

30 plus15 does not mean you have 45 amps available.

The 15 Amp "A" Generator is used internally to power the Ignition, Fuel Injectors, Fuel Pumps, Etc.
There is no External connection available to this generator.
Consider it invisible.

The 30 Amp "B" Generator is the House supply.
Some of its capacity will be needed to recharge the airframe battery.
Don't plan on using more than 20 amps on any regular basis.
10-15 amps would be a good design point.

If you need more power, there is a 40 amp external Generator option available.
It is powered from the Propeller flange.
The full 40 amps would be all yours to use as you please.

Keep in mind that this is not a Magneto-style ignition, it is fully electronic.
If you lose generator power, you lose the whole engine.
That is why there are two generators.
If the "A" generator fails, the EMU will commandeer the "B" generator leaving you with only the battery to power the panel.
If both were to fail, Your Backup-Emergency switch will allow the engine to be powered from the battery for however long the battery lasts. (30 Minutes???)

The battery does more than just start the engine. It is critical that it is in good condition in case of generator failure.
If the battery is so depleted that you need to jump-start the engine, it is not a good idea to fly until the battery issue is resolved.

The good news is that with three sources of power, so far, it is unheard of that an engine has ever quit in flight due to a triple electrical failure.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

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Re: 915iS Current Availability

by Rob Seaton » 6 years ago

Rob Seaton

3 1.32k 240

In you do lose the 30A gen you can still charge the battery and run a minimal amount of load on the 15A gen.
-turn on the Back-up switch.
-reduce your electrical load by pulling circuit breakers/turning off equipment while watching the ammeter.
-when you get a positive charge you can leave the remaining equipment on.

Thank you said by: Roger Lee,

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Re: 915iS Current Availability

by Roger Lee » 6 years ago

Roger Lee

125 5.11k 4.52k

Thanks Rob. Good info.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: 915iS Current Availability

by Micheal Fletcher » 6 years ago

Micheal Fletcher

3 3 9

Thanks Rob and Bill. Your explanations really help a lot with my electrical design.
2 questions-
1.Bill, when you say monitor the ammeter reading, - is the current information read via the fadac interface from the ECU to Garmin, or would I need to install my own shunt in order to measure the current?
2. Bill, I accept your advice / guidence on managing my current draw and to not draw more than 30A. What would happen if I were to draw more than 30A for short amount of time? Say while transmitting over radio with all lights on.

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